To minimize interference between different transmitters in a mobile radio telephone system, the transmission power of the mobile station, and in some systems the transmission power of the base station, is regulated at intervals. In power regulation, the goal is to ensure that only the power absolutely necessary to maintain satisfactory transmission of a call between a mobile station and a base station is used. By regulating the power of mobile transmissions to low levels with sufficient transmission quality, the likelihood of interference between mobile transmissions is reduced.
Another reason to maintain the power of mobile transmissions at the lowest possible level is to reduce the energy consumed at the mobile station. Accordingly, the batteries used to power portable mobile stations will require a smaller capacity. A corresponding reduction in the size of the battery needed results whereby the portable mobile stations can be made smaller.
In existing analog cellular systems, the sending power of a mobile is regulated by an order from the base station only when absolutely necessary. The ongoing conversation is disturbed when a power regulation order is sent resulting in traffic channel muting. Therefore, power regulation only occurs when the level of the signal received in the base station is outside a range defined by an upper and a lower threshold.
In such prior art systems, for example as shown in U.S. Pat. No. 4,485,486 to Webb et al, power regulation is achieved by measuring the received signal strength of transmissions from a mobile station at the corresponding base station, comparing the signal strength with an upper and a lower threshold indicative of a desired signal strength level range for proper reception, and issuing a power adjustment order from the base to the mobile if indicated by the comparison result. The monitoring is carried out at relatively infrequent intervals, typically on the order of once every five seconds, and the regulation is carried out only if indicated as being necessary.
Although modern digital systems are adequate for power regulation, system performance can be improved further. While the amount of interference is reduced over regulated analog systems, interference still presents a problem.
The present invention provides power regulation for up-link and/or down-link transmissions which maintain received signal strength values closer to the intended ideal value than achieved in known systems. Further, the present invention is adapted to modern cellular systems, in particular digital systems, where orders are transmitted on channels separated from speech. Consequently, the need to mute speech during power order transmission may be eliminated, and more frequent adjustment of power levels may be implemented.